1. Field of the Invention
The present invention relates to an internal teeth oscillating inner gearing planetary gear system.
2. Description of the Related Art
In the art, inner gearing planetary gear systems are employed widely in various reducer fields owing to the advantages of large torque transmission as well as the ability to achieve large reduction ratios.
Among reducers, internal teeth oscillating inner gearing planetary gear systems are known wherein the rotation of an input shaft is reduced in speed and delivered from an output member by oscillatingly rotating internal oscillating bodies around an external gear, the internal oscillating body having a slight difference in the number of teeth with the external gear (for example, Japanese Patent No. 2607937).
An example of the same gear system will be explained with reference to FIGS. 3 and 4.
In the drawings, a casing 1 has a first support block 1A and a second support block 1B joined together by insertion of an engaging member such as a bolt or pin (omitted in drawings) into engaging holes 2. A pinion 6 is disposed on the end of an input shaft 5. The pinion 6 meshes with a plurality of transmitting gears 7 disposed at equal angles around the input shaft 5.
Three eccentric shafts 10 are disposed in the casing 1 at equal-angled intervals (120 degree intervals) circumferentially. The eccentric shafts 10 are supported in a freely rotatable manner by bearings 8 and 9 at both axial ends and have eccentric bodies 10A and 10B in an axially midway portion . The transmitting gears 7 are joined to respective end portions of the eccentric shafts 10. The transmitting gears 7 are rotated by the rotation of the input shaft 5, to rotate each of the eccentric shafts 10.
The eccentric shafts 10 pass through eccentric holes 11A and 11B of two internal oscillating bodies 12A and 12B contained in the casing 1, respectively. Rollers 14A and 14B are disposed between outer circumferences of the two eccentric bodies 10A and 10B adjoined in the axial direction of the eccentric shafts 10 and inner circumferences of the through eccentric holes 11A and 11B of the internal oscillating bodies 12A and 12B, respectively.
An external gear 21 integrated with the end of an output shaft 20 is disposed at the central portion inside the casing 1. Internal teeth 13 formed from pins of the internal oscillating bodies 12A and 12B mesh with external teeth 23 of the external gear 21. A difference in the number of teeth between the external teeth 23 of the external gear 21 and the internal teeth 13 of the internal oscillating bodies 12A and 12B is set to be slight (for example, in a range of about 1 to 4).
The gear system operates in the following manner.
Rotation of the input shaft 5 is delivered to the transmitting gears 7 through the pinion 6. The eccentric shafts 10 are then rotated by the transmitting gears 7. The eccentric bodies 10A and 10B rotate due to rotation of the eccentric shafts 10, then the internal oscillating bodies 12A and 12B oscillatingly rotate due to the rotation of the eccentric bodies 10A and 10B. With this arrangement, through one rotation of the oscillating rotation of the internal oscillating bodies 12A and 12B, a phase of the external gear 21 which meshes with the internal oscillating bodies 12A and 12B is shifted by the difference in the number of teeth. Thus, a rotation component equivalent to the phase difference becomes the (reduction) rotation of the external gear 21, and output of reduced speed is delivered from the output shaft 20.
However, according to this known gear system, since the internal oscillating bodies 12A and 12B are oscillatingly rotated by the three eccentric shafts 10, elements such as the transmitting gears 7 and the rollers 14 must be provided corresponding to the number of the eccentric shafts 10. The number of components is therefore large, and as a result it is difficult to realize cost reduction.
Also, since the single (pinion 6 of the) input shaft 5 rotates the three transmitting gears 7 which are disposed circumferentially at equal intervals, the input shaft 5 must be located in the central portion of the gear system. Thus, for example, it is difficult to form a through-hole in the central portion of a gear system to pass wiring, piping, etc. therethrough.
Moreover, since a single internal oscillating body 12A (12B) is driven by three eccentric shafts 10, it is necessary to fabricate and assemble each member with high accuracy in order to rotate the internal oscillating body 12A (12B) smoothly in a balanced manner.